I was co-owner of a dog daycare, and employees came to me with concerns of my partner's behavior towards the dogs (very concerning). I tried to address this with my partner, but he became very hostile and refused to make any changes to the business to ensure this would not be an issue moving forward. Ultimately I dissolved the partnership and 2 out of 3 (very small company) left because we could not be apart of the company morally or ethically. I have shared this information with clients recently (post dissolution). Word got back to my ex-partner and he left a voicemail saying I was slandering him. Is it possible that I am slandering him? The ex-employees said they would be witnesses should he try to sue me.
Truth is an absolute defense. Was your ex partner abusing the animals? If so, why didn't you report the abuse to the authorities? Know that people sue other people every day, even when they do not have a good case. I hope you carry business insurance. Broad form general liability insurance is good.
I wholly agree with my colleague. Further, always couch whatever you state as "In my opinion..", as opinion statements are generally not actionable. It doesn't necessarily mean that he won't sue you, but as to defamation, you will be fine. The only other thing that you must watch out for is not to take those clients going to him if you know for sure they are his clients -- that is actionable.